1. Field of the Invention
The present invention relates to an ink supply control apparatus in a printing press, which controls an ink fountain key opening degree to assure a predetermined printing density.
2. Discussion of the Background
It has been heretofore known a control apparatus of the type that controls the ink supply in the printing press according to the density of a printed matter measured by a density measuring device so as to set a proper amount of ink to be supplied.
Specifically, a spectrophotometer, which constitutes the density measuring device, first measures a printed color bar, and calculates a density difference in each color with respect to a target printed matter or a reference density value. Signals representative of the calculated density difference are then transmitted to the control apparatus that in turn corrects the opening degree of an ink fountain key of the printing press by an amount or degree corresponding to a correction value for the opening degree, which correction value being determined from the aforesaid density difference, thereby obtaining a proper amount of ink to be supplied in the printing press.
However, according to the control apparatus of the above conventional type, the ink fountain key opening degree is corrected to such an amount or degree which is intended for printing a printed matter with a target density from the start of the printing. Because of this, it takes a relatively long period of time to obtain a key opening degree correction effect.
Specifically, a series of rollers are arranged in plural stages between an ink fountain with ink to be supplied and a plate cylinder on which a printing plate is mounted. According to this arrangement, it is unlikely to supply a proper amount of ink onto the printing plate on the plate cylinder immediately after the correction of the ink fountain key opening degree to a degree corresponding to a target density. This results in a great number of sheets lost before obtaining the printed matter with the target density. The number of the sheets lost depends on the type of ink, the pattern of the printing plate, or the like, but sometimes reaches about 150 to 200. In actual operation, the loss of a relatively large number of sheets poses a serious problem.
The present invention has been conceived to address the above problem. Specifically, it is an object of the present invention to provide an ink supply control apparatus that is capable of efficiently limiting the number of sheets lost before the printed matter reaches a target density.
According to the present invention, there is provided an apparatus for controlling ink supply by varying the opening degree of an ink fountain key according to a measured density of a printed matter that includes a control means for determining a reference correction value of the opening degree of the ink fountain key according to the density difference between a target density of the printed matter or a reference density and the measured density, and determining a correction value by multiplying the reference correction value by a coefficient having a value of more than 1. The control means controls the ink fountain key according to the correction value of the opening degree of the ink fountain key until the number of sheets printed from the start of the printing exceeds a predetermined number, and controls the ink fountain key according to the reference correction value after the number of sheets printed exceeds said predetermined number.
According to the apparatus having the above arrangement, the opening degree of the ink fountain key is corrected in such a manner as to be larger than the ink fountain key opening degree adapted for the target density when the target density is larger than the measured density during an initial stage from the start of the printing, and to be smaller than the same when the target density is smaller than the measured density. That is, the correction of the ink fountain key opening degree can be performed in such a manner as to enhance the correction effect during the initial stage. As a result, the number of sheets lost before the printed matter reaches the target density can be limited.
The coefficient preferably has a value variable according to a different block of a predetermined number of sheets, and the positive and the negative in value of the reference correction value. Through this coefficient, it is possible to set a proper coefficient according to the type of ink, type of a print sheet, temperature, moisture, type of a printing press, printing speed, percentage of moisture content, or other printing conditions.